1. Field of the Invention
The present invention generally relates to a valve for injecting a sample into a flowing stream and, more particularly, to a multi-position rotary valve for injecting a liquid sample into a high pressure stream of liquid by means of a conventional low pressure volumetric syringe without loss of sample and in a quantity which is quantitatively one of three.
2. Description of the Prior Art
In the field of liquid chromatography, the contents of a liquid sample, which consists of unknown quantities of compounds, is analyzed by injecting the sample in a stream of a suitable eluting solvent diluent, which passes through the chromatographic column and therefrom to an approprite detector. Typically, the solvent from an appropriate source is pumped to the column by a pump, e.g., a constant flow pump. Modern columns generate relatively high back pressures under normal operation, e.g. 2000 psi and above.
For many years the fixed loop sample injection valve has been used in high pressure liquid chromatography because of its convenience of use, reliablity and precision. Its major disadvantages are that a considerable amount of sample is wasted in the process of loading to insure that the sample loop is completely filled. Also, sample size can be changed only by changing the loop size. Syringe injection methods have been employed to circumvent these problems but not as satisfactorily as is now demonstrated in the present invention.